He was being kept in a 2.5 gal tank, no filter, but had a heater and an under gravel air filter thing, as well as a light.. I was doing frequent changes of the water until I get the 10 gallon setup cycled for him.

Either way - shortly after I posted that, I did a 100% water change, as well as a salt bath. When I got him back in the tank, he was swimming around like a maniac - which I figured just meant he was happy. Well a couple minutes later he got really lethargic - which I figured meant he was worn out...

Well, a few minutes later I caught him wedged up in the corner of the tank between the wall and the thermometer, with his head above water. I quickly got him out of the tank and put him in the cup he came in with some pre-treated water I keep in an old spring water jug. He is still alive, but seems very lethargic. I can't honestly say how old he is since I have only had him a month - and although he has gotten a bit bigger, he was what I would guess is an adult size when I got him.

He seemed fine and was eating great earlier today. I don't know if the scale issue is something related to his frantic swimming/lethargy or what.

Any help would be greatly appreciated - I am very new to keeping fish (ask me about dog or cat health issues and I can answer pretty much everything though :p), but I don't want him to suffer because I am uneducated on fish.